Photoionization transition Cr3+ → Cr2+ in GaAs : Cr

Abstract
The photoionization absorption spectrum of the strongly Cr-doped GaAs samples was measured in the energy region 5 500-11 000 cm-1 under hydrostatic pressure up to 9 kbar at 300 K and 77 K. The EPR measurements with 1.09 μm laser excitation shows that this absorption is due to the charge transfer Cr3+ → Cr 2+ transitions. The theoretical model which takes into account the lattice relaxation effect is used to fit the photoionization absorption curves. The values of optical ionisation energy EO, thermal ionization energy E T and their pressure dependence are obtained. The relaxation energy ER = EO - ET is found as about 0.17 eV and the absorption cross section as about 5 x 10 -17 cm2